The present invention relates generally to well drilling operations and, more particularly, to well drilling operations using magnetic ranging while drilling to reduce the footprint of drilling operations and/or efficiently utilize available space by densely packing wells.
In many drilling operations, it may be necessary or desirable to closely space a plurality of wells to reduce environmental impact and/or to efficiently utilize available space. For example, space is generally at a premium on offshore production platforms because there is a limited area available for wellheads. Accordingly, the wells are typically packed together in a closely spaced configuration. Indeed, such platforms typically include many closely spaced wells that extend vertically under the platform to a certain depth before branching out into deviated and horizontal trajectories. The region under the platform wherein the wells are closely spaced may extend for a substantial distance (e.g., several hundred meters) before a “kick-off” point, where the wells deviate and extend away from the tightly spaced region.
Including a large number of wells in a small space, such as the closely spaced region beneath the offshore platform discussed above, can increase the potential for collisions between a drill bit and an existing well. Thus, wells are generally separated by a safe minimum distance to avoid or substantially reduce the risk of such collisions. Hence, the number of wells (or “slots”) that can be accommodated within a defined area (e.g., a platform) is generally limited by uncertainties in the wells' trajectories in the formation. Traditionally, uncertainties in the positions of existing wells and the uncertainty in the drill bit position are related to the accuracy of measurement while drilling (MWD) and direction and inclination (D&I) measurements. With conventional practice, uncertainty in well position increases as the depth of the well increases, which defines an ellipse of uncertainty. This uncertainty arises from the limited accuracy of the MWD and D&I measurements, and from the limited accuracy of any wireline surveys that might have been performed after the wells were cased.